Silicon carbide (SiC) is a third-generation semiconductor—wide band gap semiconductor material, with advantages of wide band gap, high critical breakdown field strength, and high thermal conductivity. It is an ideal material for high-voltage, high-power semiconductor devices. SiC power electronic devices are at the heart of next-generation high-efficiency power electronics technology. Compared to Si MOSFETs, SiC MOSFETs have lower on-resistance, higher switching voltage, higher application frequency, and better temperature performance, making them ideal for power switching applications. The integrated manufacturing process of SiC MOSFET devices, especially the gate dielectric process, is a hot topic of current research.
SiC is the only compound semiconductor from which SiO2 can be thermally grown, which allows SiC to realize the device structure of all Si MOS devices. The thermal oxidation of SiC requires a higher oxidation temperature than Si, and the oxidation temperature is as high as 1300° C. At present, the mainstream SiC oxidation process mainly uses an electric resistance heating furnace. The main principle is based on the reaction of silicon carbide with oxygen molecules, but this method of oxidation with oxygen molecules easily causes defects such as residual carbon clusters, Si—O—C bonds, C dangling bonds, and oxygen vacancies at the interface, and the interface quality is degraded, resulting in a decrease in mobility, as shown in FIG. 1. Especially at such high temperatures, in addition to interface oxidation, it also causes interface damage and reduces oxidation efficiency.
In recent years, researchers have proposed a method of oxidizing SiC by plasma at low temperatures, which improves the interface quality to some extent. However, the oxidation efficiency of the method is low. Especially in the case where a thick SiO2 layer is required, the oxidation time is long, and at the interface between SiC and SiO2, SiC and SiO2 are still in a thermodynamic equilibrium state, resulting in unsatisfactory interface quality.
In addition, experiments have shown that the oxidation rate of silicon carbide in different crystal orientations varies widely. On the Si plane, the plane perpendicular to the a-axis has an oxidation rate even 3-5 times that of the plane perpendicular to the c-axis. If the thermal oxidation process is used to form the gate oxide of the LIMOS structure, the thickness of the oxide layer on the sidewall is 3-5 times that of the bottom, as shown in FIG. 2, which prevents the device from turning on normally under forward bias.
This is because the channel is a longitudinal channel formed from the sidewall, and a higher gate voltage VG is required in order for the device to be normally turned on. However, since the thermal oxidation growth rate of SiO2 on the sidewall is several times the rate of the bottom oxidation, the gate voltage of the channel region on the sidewall of the device does not reach the threshold voltage when the gate voltage reaches the maximum value of the safe operating voltage of the gate oxide, so the device cannot be turned on and the forward characteristic cannot be obtained. If the gate voltage is continuously increased, the stability of the bottom gate oxide is deteriorated, causing the bottom oxide layer to break down in advance and the device will not work properly. Therefore, forming a uniform gate oxide layer with a low interface state is the key to making a grooved gate MOSFET device.